The ancient Greek mathematician Euclid proved in his Elements of Geometry that there are only five Platonic solids – the regular tetrahedron (four sides that are equilateral triangles), the cube (six ...

Properties of symmetry: - Students may notice symmetry in the isosceles and equilateral triangles and non-symmetry in the scalene triangles Informal recognition of these properties may be helpful in ...

Big Idea – We can describe, measure, and compare spatial relationships. to build on students' knowledge of triangle and develop students' reasoning with properties of different classes of triangles to ...